President Joko Widodo has visited remote Indonesian islands on a warship in an apparent show of force following clashes with Chinese vessels and growing fears Beijing is seeking to stake a claim in nearby waters.

Mr Widodo led a high-level delegation, including the Foreign Minister and armed forces chief, to the Natuna Islands in the South China Sea, arriving at a navy base before being escorted to the warship as fighter jets buzzed overhead and military vessels performed manoeuvres off the coast.

At a meeting of ministers and security force chiefs on the warship, which last week detained a Chinese trawler and its crew in Indonesian waters, the President ordered defences around the Natunas to be stepped up.

“I asked the military and the maritime security agency to better guard the seas,” he said.

A picture released by the Government showed Mr Widodo standing next to a gun turret on deck, flanked by the military chief and ministers.

Before the trip, Security Minister Luhut Panjaitan said it was aimed at sending a “clear message” that Indonesia was “very serious in its effort to protect its sovereignty”.

Beijing asserts sovereignty over almost the entire strategically important South China Sea, and regional tensions are mounting due to Chinese island building and ahead of a UN-backed tribunal’s ruling on a Philippine challenge to China’s claims.

Overlapping claims

Unlike some of its South-East Asian neighbours, Indonesia has long maintained it has no maritime disputes with China in the sea and has no overlapping claims to reefs or islets there.

But Beijing’s claims overlap Indonesia’s exclusive economic zone — waters where a state has the right to exploit resources — around the Natunas, and Mr Widodo’s visit came after a sharp escalation in maritime clashes between Indonesian vessels and Chinese fishing boats in the area.

Foreign ministry spokeswoman Hua Chunying on Thursday reiterated Beijing’s position that China and Indonesia “have no territorial disputes” and that China does not object to Indonesia’s sovereignty over the Natuna Islands.

But she added that “China and Indonesia have overlapping claims over maritime rights of some part of the waters in the South China Sea”.

The term “overlapping claims” was also used in a Chinese statement earlier this week.

Analysts say the language indicates Beijing is taking a tougher stance by openly saying that China and Indonesia have competing maritime claims.

The growing tensions come after a senior US State Department official warned this week that China is using its fishing fleets with armed escorts to bolster maritime claims.

The latest confrontation between Beijing and Jakarta came last week when the Indonesian navy seized a Chinese-flagged fishing vessel and detained its crew for allegedly operating illegally in Natuna waters. It was the third such skirmish between vessels from the two countries in the area this year.

Beijing protested and claimed that one fisherman was injured after Indonesian vessels fired warning shots. Jakarta says none of the crew were hurt.

Mr Widodo’s visit to the islands, which are located west of Borneo, was his first as President.

The Natuna waters are home to oil and gas deposits as well as fishing grounds.

Confrontations between Indonesian and Chinese vessels around the Natunas have increased since Jakarta launched a crackdown on illegal fishing in 2014.

Vietnam, China, Malaysia have eyes on the prize

Explore the conflicting territorial claims in the South China Sea

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Rich in resources and traversed by a quarter of global shipping, the South China Sea is the stage for several territorial disputes that threaten to escalate tensions in the region.

At the heart of these disputes are a series of barren islands in two groups – the Spratly Islands, off the coast of the Philippines, and the Paracel Islands, off the coasts of Vietnam and China.

Both chains are essentially uninhabitable, but are claimed by no fewer than seven countries, eager to gain control of the vast oil and gas fields below them, as well as some of the region’s best fishing grounds.

Indonesia, Malaysia and Brunei have made claims to part of the Spratlys based on the internationally recognised Exclusive Economic Zone (EEZ), which extends 200 hundred nautical miles from a country’s coastline.

Based on the EEZ, the Philippines has the strongest claim on the Spratlys and their resources, with its EEZ covering much of the area.

However the lure of resources, and prospect of exerting greater control over shipping in the region, means that greater powers are contesting the Philippines’ claims.

China has made extensive sovereignty claims on both the Spratlys and the Paracels to the north, based largely on historic claims outlined in a map from the middle part of the 20th Century known as the ‘Nine Dash Map’.

Taiwan also makes claims based on the same map, as it was created by the nationalist Kuomintang government, which fled to Taiwan after the communists seized power in China.

Vietnam also claims the Spratlys and the Paracels as sovereign territory, extending Vietnam’s EEZ across much of the region and bringing it into direct conflict with China.

There have been deadly protests in Vietnam over China’s decision to build an oil rig off the Paracels.

One Chinese worker in Vietnam was killed and a dozen injured in riots targeting Chinese and Taiwanese owned factories, prompting 3,000 Chinese nationals to flee the country.

EEZ can only be imposed based on boundaries of inhabitable land, and this has prompted all the countries making claims on the region to station personnel, and in some cases build military bases out of the water, to bolster their claim.

Building and protecting these structures has resulted in a series of stand-offs between countries in the region, each with the potential to escalate.

China has been leading the charge with these installations, and has deployed vessels to the region to protect their interests.

Chinese coast guard vessels have used a water cannon on Vietnamese vessels, as well as blockading an island where the Philippines has deployed military personnel.